Occlusion detection method and system for ambulatory drug infusion pump

ABSTRACT

A method of detecting an occlusion within a flexible infusion tube by measuring samples indicative of pressures relative to instances in time. Difference values for the samples are created. The difference values are compared to percentages of other difference values. When appropriate, an occlusion signal is generated in response to a comparison of a difference value to a percentage of another difference value.

RELATED APPLICATIONS

This application is a divisional of co-pending U.S. application Ser. No.09/708,112 filed Nov. 7, 2000, which application is incorporated hereinby reference and made a part hereof, and upon which a claim of priorityis based.

DESCRIPTION TECHNICAL FIELD

The invention relates generally to monitoring fluid flow, and moreparticularly, to detecting upstream fluid occlusions in an intravenousfluid administration system.

BACKGROUND OF THE INVENTION

Fluid delivery systems for infusing parenteral fluids are commonly usedin hospitals and typically include an inverted bottle or bag or othermeans of supply of parenteral fluid, an intravenous (IV) administrationset and an infusion pump for controlled delivery to a vascular system ofa patient. The fluid administration set typically includes a flexibleinfusion tube, a drip chamber, injection sites among other components,and a catheter mounted to the distal end of the flexible infusion tubeadapted to be inserted into the patient's blood vessel. Commonly, thepump is of a peristaltic type in which a plurality of fingers, rollers,or other devices sequentially constrict the tubing along a moving regionof occlusion to move fluid through the tubing.

One of the difficulties of infusion systems is the evaluation of thecondition of the fluid flow upstream of the pump. Where an occlusion ofthe infusion tube exists upstream of the pump, the pump will not succeedin infusing the parenteral fluid to the patient even though the pump maycontinue to operate. Similarly, when the parenteral fluid supply becomesdepleted, the pump may also continue to operate, however no parenteralfluid will be administered to the patient.

One previous method for detecting a decrease in the fluid supply or anupstream occlusion was visual observation of a drip chamber. However,visually verifying the existence of drops places an undesirable burdenon the hospital staff.

In infusion systems utilizing peristaltic pumps, detection of upstreamocclusions has been accomplished through the use of an opto-electricdrop detector combined with a drip chamber. The opto-electric dropdetector detects upstream occlusions, such as occlusions caused by aclamp or kink in the upstream tubing, by detecting an absence of drops.However, the opto-electric drop detector has several disadvantages.Significant movement of the IV administration set can cause a surplus ofdrops to fall from the drop former or can interrupt the drop formation,thereby causing inaccurate drop counts and false alarms. Ambient lightcan also interfere with the accuracy of an optical drop sensor.

Another method for detecting upstream occlusions is to incorporate apressure sensor into the pumping mechanism of the infusion pump. In onesuch device, a pressure transducer is placed in the middle of thepumping area, allowing direct measurement of the pressure in the pumpsegment of the fluid tube. The resulting measurement is indicative ofthe inlet pressure. However, this method can adversely affect flowuniformity and may require substantial modifications to the pumpingmechanism.

Pump systems have been disclosed that include a downstream pressuresensor used for detecting improper fluid communication with the patient.Such systems include U.S. Pat. No. 4,743,228 to Butterfield; U.S. Pat.No. 4,460,355 to Layman; U.S. Pat. No. 4,534,756 to Nelson; and U.S.Pat. No. 5,356,378 to Doan.

In operation, peristaltic pump mechanisms sequentially occlude thepumping segment of the tube, also known as the pumping control segment,to alternately expose the pumping segment to fluid communication withthe upstream and downstream portions of the infusion tube. The pumpingsegment is at upstream pressure when exposed to the upstream portion ofthe fluid line. When the pumping segment is subsequently exposed to thedownstream portion, the fluid within the pumping segment, which was atupstream pressure, causes a change in pressure, i.e., a pressuredifference, as the pumping segment pressure equalizes with thedownstream portion.

There have been pump systems with downstream pressure sensors that haveutilized analysis of such pressure differences to detect upstreamocclusions. If a large negative pressure difference occurs, an upstreamocclusion is presumed. However, pumping into high downstream pressurescan create pressure waveform conditions, including drops in pressure,that mimic the appearance of true upstream occlusions. Additionally,pressure sensors may exhibit substantial offset errors that can alsomimic upstream occlusion conditions. Pressure sensors used with infusionsystems may express variance in their readings that can deviatesubstantially from the desired values. Such variances, which may beproduced by temperature differences or other factors such as thecomposition of the infusion tube, can cause false alarms. These falsealarms detract from the usefulness of an occlusion detection system.While in some cases these variances may be reduced through compensationcircuits or closer tolerances on various mechanical and circuitelements, these approaches may substantially complicate the device.

Accordingly, it is desirable to use an upstream pressure sensor havingaccuracy requirements less stringent than absolute values or thresholdvalues while avoiding false alarms.

Hence, those skilled in the art have recognized the need for a infusiontube monitoring system that can automatically detect upstream infusiontube occlusions while minimizing false alarms. Additionally, thoseskilled in the art have recognized a need to reduce the cost of a systemcapable of determining such upstream infusion tube conditions. Thepresent invention fulfills these needs and others.

SUMMARY OF THE INVENTION

Other advantages and aspects of the present invention will becomeapparent upon reading the following description of the drawings anddetailed description of the invention.

Accordingly, the present invention provides a method and system for thedetection of upstream occlusions in flexible infusion tubing so as toallow for the minimization of false occlusion alarms. The method is usedwithin an occlusion detection system. The occlusion detection system fordetecting occlusions inhibiting a fluid flowing in a tube adapted forconnection to a fluid pump has a pressure sensor for releasableattachment to the tube upstream of the fluid pump for monitoring anegative pressure condition. The occlusion detection system contains atransducer operably attached to the pressure sensor, the transducerconverts the monitored negative pressure condition in a fluid tube intoa usable signal. The occlusion detection system further includes analarm module that is responsive to a signal indicating that the negativepressure condition is outside an acceptable range.

In one aspect of the present invention, the transducer is attached tothe pressure sensor that makes contact with the flexible infusion tube.Several types of transducers may be used with the occlusion detectionsystem. These include, but are not limited to, a force sensing resistor,a piezoresistive sensor, a piezoelectric sensor, a diaphragm pistongauge, a bending beam gauge, a strain gauge, a hall-effect sensor, a ¼bridge strain gauge, a ½ bridge strain gauge, or a full bridge straingauge. In another aspect of the present invention, the fluid pump may beselected from the group consisting of a peristaltic pump, a roller pump,an expulsor pump, a finger pump and a piston cassette pump. In yetanother aspect of the present invention, the pressure sensor can becalibrated with a calibration gauge. In some applications, the signalingof an upstream occlusion may be over a network.

In addition to the above, the method of detecting an occlusion within aflexible infusion tube includes the steps of measuring a first sampleindicating a pressure in the tube relative to a first instance in time;measuring a second sample indicating a pressure in the tube relative toa second instance in time; measuring a third sample indicating apressure in the tube relative to a third instance in time; creating afirst difference value of the first sample to the second sample;creating a second difference value of the second sample to the thirdsample; comparing the first difference value to a percentage of thesecond difference value; and generating an occlusion signal in responseto the step of comparing the first difference value to the seconddifference value.

In yet another aspect of the present invention, the method of detectingan occlusion within a flexible infusion tube includes the steps ofmeasuring a first sample indicating a pressure in the tube relative to afirst instance in time; measuring a second sample indicating a pressurein the tube relative to a second instance in time; creating a firstdifference value of the first sample to a second sample; comparing thefirst difference value to a percentage of a second difference value; andgenerating an occlusion signal in response to the step of comparing thefirst difference value to a second difference value.

In another aspect of the present invention, the system for detecting anocclusion within a flexible infusion tube includes a measuring devicefor measuring a first sample indicating a pressure in the tube relativeto a first instance in time; the measuring device also measuring asecond sample indicating a pressure in the tube relative to a secondinstance in time; the measuring device also measuring a third sampleindicating a pressure in the tube relative to a third instance in time;the measuring device also creating a first difference value of the firstsample to the second sample; the measuring device also creating a seconddifference value of the second sample to the third sample; the measuringdevice also comparing the first difference value to a percentage of thesecond difference value; and an alarm module generating an occlusionsignal in response to the measuring device also comparing the firstdifference value to the second difference value.

In yet another aspect of the present invention, the system for detectingan occlusion within a flexible infusion tube includes a measuring devicefor measuring a first sample indicating a pressure in the tube relativeto a first instance in time; the measuring device also measuring asecond sample indicating a pressure in the tube relative to a secondinstance in time; the measuring device also creating a first differencevalue of the first sample to a second sample; the measuring device alsocomparing the first difference value to a percentage of a seconddifference value; and an alarm module generating an occlusion signal inresponse to the measuring device also comparing the first differencevalue to the second difference value.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become apparent from a consideration of the subsequentdetailed description presented in connection with the accompanyingdrawing, in which:

FIG. 1 is a cross-sectional view of a pump containing the upstreamocclusion system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible of embodiments in many differentforms, there is shown in the drawings and will herein be described indetail a preferred embodiment of the invention. The present disclosureis to be considered as an exemplification of the principles of theinvention and is not intended to limit the broad aspect of the inventionto the embodiment illustrated.

Referring now to FIG. 1, a pump 10 is shown which includes a motor 12, acamshaft 14, a tubing set 16, and an upstream occlusion system 18.

The motor 12 is operably connected to and facilitates the movement ofthe camshaft 14.

Camshaft 14 accommodates a plurality of pumping fingers 20. The pumpingfingers 20 facilitate the pumping action that maintains the fluid flow.The pumping action results from the motor 12 engaging the camshaft 14,the motor 12 then imparting rotational movement to the camshaft 14. Oncethe camshaft 14 is in rotational movement, the pumping fingers 20sequentially apply waveform pressure on the tubing set 16.

The tubing set 16 preferably consists of a flexible infusion tube. Thetubing set 16 originates from the fluid supply, preferably anintravenous solution bag. The tubing set 16 enters pump 10 and passesthrough the upstream occlusion system 18. The tubing set 16 passesthrough the upstream occlusion system 18 prior to having waveformpressure applied by the pumping fingers 20.

The upstream occlusion system 18 is composed of a pressure sensor 22 forreleasable attachment to the tubing set 16 upstream of the pumpingfingers 20, a transducer 24 operably attached to the pressure sensor 22,and an alarm module 26 for signaling that the occlusion has occurred inresponse to the alarm module 26 receiving the useable signal from thetransducer 24.

The pressure sensor 22 is for monitoring a negative pressure condition.In a preferred embodiment, the pressure sensor 22 is releasably attachedto the tubing set 16 upstream of the pump 10.

The transducer 24, operably attached to pressure sensor 22, preferablyconverts the monitored negative pressure condition in the tubing set 16into a usable signal. The transducer 24 may be a force sensing resistor,a piezoresistive sensor, a piezoelectric sensor, a diaphragm pistongauge, a bending beam gauge, a strain gauge, a hall-effect sensor, a ¼bridge strain gauge, a ½ bridge strain gauge, or a full bridge straingauge.

The alarm module 26 generates a signal indicating that the negativepressure condition is outside an acceptable range.

The first step in detecting an occlusion in a tubing set is obtainingthe initial voltage of the tubing set at the start of a pumping cycle.Preferably, detecting an occlusion in tubing set 16 at the start of thepumping cycle of pump 10 begins where the pressure sensor 22 measuresthe initial voltage of the tubing set 16. The initial voltage is thevoltage at the start-up of pump 10. The pressure sensor 22 then measuresboth the high voltage of the tubing set 16 for the first pumping cycleof pump 10 and the low voltage of the tubing set 16 for the firstpumping cycle of pump 10.

The transducer 24 converts these voltage readings into signals usablefor the pump 10 in determining the presence of an upstream occlusion.The presence of an upstream occlusion at pump start-up is determined bywhere the initial voltage at pump start-up falls in a particular rangeof values. The range of values is composed of percentages of the highvoltage determined for the first pumping cycle.

The pump 10 is calibrated without calibration software, only requiring acalibration gauge. The calibration gauge simulates an upstreamocclusion. A potentiometer is used to set the upstream occlusionsystem's output to the proper limits of the operating range.

In one example, if the initial voltage at pump start-up is within 10% ofthe high voltage value for the first pumping cycle, i.e., where thedifference between the initial voltage and the low voltage for the firstpumping cycle is less than 10% of the difference between the highvoltage and the low voltage for the first pumping cycle, then the pump10 generates an occlusion signal if a high voltage value of a subsequentpumping cycle subtracted from the high voltage value of a first pumpingcycle is greater than about 40 percent of the high voltage value of afirst pumping cycle minus the initial low voltage value of a firstpumping cycle.

In another example, if the initial voltage at pump start-up is within50% of the low voltage value for the first pumping cycle, i.e., wherethe difference between the initial voltage and the low voltage for thefirst pumping cycle is less than 50% of the difference between the highvoltage and the low voltage for the first pumping cycle, then the pump10 generates an occlusion signal if a high voltage value of a subsequentpumping cycle subtracted from the initial high voltage value of a firstpumping cycle is greater than about 20 percent of the initial highvoltage value of a first pumping cycle minus the initial low voltagevalue of a first pumping cycle.

In yet another example, if the initial voltage at pump start-up does notfall within a prescribed range for the first pumping cycle, then thepump 10 generates an occlusion signal if a high voltage value of asubsequent pumping cycle subtracted from the initial high voltage valueof a first pumping cycle is greater than about 30 percent of the initialhigh voltage value of a first pumping cycle minus the initial lowvoltage value of a first pumping cycle.

In still another example, once pump 10 has completed a predeterminednumber of cycles, the pump 10 will generate an occlusion signal if thedifference of the initial high voltage value of a first pumping cycleand a high voltage value of a subsequent pumping cycle is greater thanabout 25 percent of the initial high voltage value of a first pumpingcycle minus the initial low voltage value of a first pumping cycle.

In a further example, in order to avoid false occlusion alarm signals asthe contents of the fluid bag of administration system are depleted, thepump 10 will generate an occlusion signal if after completing apredetermined number of cycles the difference of the initial highvoltage value of a first pumping cycle and the high voltage values of atleast about every eighth pumping cycle is greater than about 15 percentof the initial high voltage value of a first pumping cycle minus theinitial low voltage value of a first pumping cycle.

Preferably, if an occlusion signal is generated, the pump 10discontinues the pumping cycle. Once the pumping cycle is discontinued,the pump 10 must be reset manually. Upon restart, the pump 10 will, forexample, generate an occlusion signal if the difference of the initialhigh voltage value prior to occlusion minus the initial high voltagevalue of the first pumping cycle after occlusion is greater than apercentage of the initial high voltage value of a first pumping cycleprior to occlusion minus the initial low voltage value of a firstpumping cycle prior to occlusion.

In view of the foregoing, it can be appreciated that the presentinvention provides a simple, low cost apparatus and method for detectingupstream occlusions in the tubing set of an IV fluid administrationsystem without the necessity of modifying existing pump mechanisms.Although preferred and alternative embodiments of the invention havebeen described and illustrated, the invention is susceptible tomodifications and adaptations within the ability of those skilled in theart and without the exercise of inventive faculty. Thus, it should beunderstood that various changes in form, detail and usage of the presentinvention may be made without departing from the spirit and scope of theinvention.

We claim:
 1. A method of detecting an occlusion within a flexibleinfusion tube, comprising the steps of: measuring a first sampleindicating a pressure in the tube relative to a first instance in time;measuring a second sample indicating a pressure in the tube relative toa second instance in time; measuring a third sample indicating apressure in the tube relative to a third instance in time; creating afirst difference value of the first sample to the second sample;creating a second difference value of the second sample to the thirdsample; comparing the first difference value to a percentage of thesecond difference value; and generating an occlusion signal in responseto the step of comparing the first difference value to the seconddifference value.
 2. The method of claim 1 wherein the occlusion signalis generated when the first difference value is greater than thepercentage of the second difference value.
 3. The method of claim 2wherein the first sample is a first voltage level, wherein the secondsample is a second voltage level, and wherein the third sample is athird voltage level.
 4. The method of claim 3 wherein the measuringfurther comprises: measuring a start sample for a pumping cycle;measuring a high sample for the pumping cycle; and measuring a lowsample for the pumping cycle.
 5. The method of claim 4 wherein eachmeasured sample is recorded.
 6. The method of claim 5 wherein the startsample is a start voltage level, wherein the high sample is a highvoltage level, and wherein the low sample is a low voltage level.
 7. Themethod of claim 6 wherein the occlusion value is selected from a groupconsisting of a high voltage difference value equation, a low voltagedifference value equation, a median voltage difference value equation, asteady state difference value equation, an end of bag difference valueequation, and a restart difference value equation.
 8. The method ofclaim 7 wherein the high voltage difference value equation determinesocclusion presence where a high voltage value of a subsequent pumpingcycle subtracted from the initial high voltage value of a first pumpingcycle is greater than about 40 percent of the initial high voltage valueof a first pumping cycle minus the initial low voltage value of a firstpumping cycle.
 9. The method of claim 8 wherein the low voltagedifference value equation determines occlusion presence where a highvoltage value of a subsequent pumping cycle subtracted from the initialhigh voltage value of a first pumping cycle is greater than about 20percent of the initial high voltage value of a first pumping cycle minusthe initial low voltage value of a first pumping cycle.
 10. The methodof claim 9 wherein the median voltage difference value equationdetermines occlusion presence where a high voltage value of a subsequentpumping cycle subtracted from the initial high voltage value of a firstpumping cycle is greater than about 30 percent of the initial highvoltage value of a first pumping cycle minus the initial low voltagevalue of a first pumping cycle.
 11. The method of claim 10 wherein thesteady state difference value equation determines occlusion presencewhere the difference of the initial high voltage value of a firstpumping cycle and a high voltage value of a subsequent pumping cycle isgreater than about 25 percent of the initial high voltage value of afirst pumping cycle minus the initial low voltage value of a firstpumping cycle.
 12. The method of claim 11 wherein the steady statedifference value equation determines occlusion presence may be used todetermine occlusion for multiple pumping cycles after: a high voltagedifference value equation; a low voltage difference value equation; or amedian voltage difference value equation.
 13. The method of claim 12wherein the end of bag difference value equation determines occlusionpresence where the difference of the initial high voltage value of afirst pumping cycle and the high voltage values of at least about everyeighth pumping cycle is greater than about 15 percent of the initialhigh voltage value of a first pumping cycle minus the initial lowvoltage value of a first pumping cycle.
 14. The method of claim 13wherein the restart difference value equation determines occlusionpresence where the difference of the initial high voltage value prior toocclusion minus the initial high voltage value of the first pumpingcycle after occlusion is greater than a percentage of the initial highvoltage value of a first pumping cycle prior to occlusion minus theinitial low voltage value of a first pumping cycle prior to occlusion.15. The method of claim 14 wherein the percentage of the initial highvoltage value of a first pumping cycle prior to occlusion minus theinitial low voltage value of a first pumping cycle prior to occlusion isfrom at least about 15 percent to about 40 percent.
 16. The method ofclaim 15 wherein the percentage of the initial high voltage value of afirst pumping cycle prior to occlusion minus the initial low voltagevalue of a first pumping cycle prior to occlusion is the percentage ofthe initial high voltage value of a first pumping cycle minus theinitial low voltage value of a first pumping cycle for the equation thatdetermined occlusion.
 17. The method of claim 16 wherein the equationsto determine an occlusion comprise a high voltage difference valueequation, a low voltage difference value equation, a median voltagedifference value equation, a steady state difference value equation, anend of bag difference value equation, and a restart difference valueequation.
 18. The method of claim 17 wherein the pumping cycle may bereset.
 19. The method of claim 18 wherein the restart equation is usedafter the pumping cycle is reset.
 20. The method of claim 19 wherein thedata is stored in electronically readable memory.
 21. The method ofclaim 20 wherein the signal indicating an occlusion is sent over anetwork.
 22. An occlusion detection system for detecting occlusionsinhibiting a fluid flowing in a tube adapted for connection to a fluidpump, the occlusion detection system comprising: a pressure sensor forreleasable attachment to the tube upstream of the fluid pump formonitoring a negative pressure condition; a transducer operably attachedto the pressure sensor, the transducer converting the monitored negativepressure condition in a fluid tube into a usable signal; and an alarmmodule for signaling that the occlusion has occurred in response to thealarm module receiving the useable signal from the transducer, thesignal indicating that the negative pressure condition is outside anacceptable range.
 23. The system according to claim 22 wherein thetransducer is a force sensing resistor, a piezoresistive sensor, apiezoelectric sensor, a diaphragm piston gauge, a bending beam gauge, astrain gauge, a hall-effect sensor, a ¼ bridge strain gauge, a ½ bridgestrain gauge, or a full bridge strain gauge.
 24. The system according toclaim 23 wherein the fluid pump is selected from the group consisting ofa peristaltic pump, a roller pump, an expulsor pump, a finger pump and apiston cassette pump.
 25. The system according to claim 24 wherein thepressure sensor can be calibrated with a calibration gauge.
 26. Thesystem according to 25 wherein the signaling of an upstream occlusionmay be over a network.